1. Field of Invention
The present invention relates to metal-air fuel cell battery systems designed to produce electrical power from metal-fuel tape transported over the cathode structures of the system, and more particularly to such systems employing movable cathode structures having low friction characteristics.
2. Brief Description of the Prior Art
In copending U.S. application Ser. No. 08/944,507 entitled xe2x80x9cHigh-Power Density Metal-Air Fuel Cell Battery System, Applicants disclose several types of novel metal-air fuel cell battery (FCB) systems. During power generation, metal-fuel tape is transported over a stationary cathode structure in the presence of an ionically-conductive medium, such as an electrolyte-impregnated gel (i.e. electrolyte-impregnated film). In accordance with well known principles of electrochemistry, the transported metal-fuel tape is oxidized as electrical power is produced from the system.
FCB power generation systems of the type disclosed in U.S. application Ser. No. 08/944,507 have numerous advantages over prior art electro-chemical power generation devices including, for example, the generation of electrical power over a range of output voltage levels selectable to particular electrical load conditions. Also, the oxidized metal-fuel tape can be reconditioned (i.e. recharged) during battery charging cycles carried out during electrical power generation, as well as separately therefrom.
In copending application Ser. No. 09/074,337 entitled xe2x80x9cMetal-Air Fuel-Cell Battery Systemsxe2x80x9d filed May 7, 1998, Applicants disclose several novel systems and methods for reconditioning oxidized metal-fuel tape used in FCB systems. In theory, such technological improvements enable metal-fuel tape to be quickly recharged in an energy efficient manner for reuse in electrical power generation cycles. Such advances offer great promise in many fields of endeavor requiring electrical power.
The greatest limitation, however, with prior art metal-air FCB systems is that, as the metal-fuel tape is being transported over the stationary cathode structures within such systems, frictional (e.g. shear) forces are generated, causing a number of problems to arise.
One problem is that such frictional forces cause an increase in the amount of electrical power required to transport the metal-fuel tape through the system.
Another problem is that such frictional forces cause metal-oxide particles to be shed from metal-fuel tape during transport and to become embedded within the porous structure of the cathode, thereby preventing ionic transport between the cathode and ionically-conductive medium (i.e. referred to as xe2x80x9cblindingxe2x80x9d), and increasing the likelihood of damage (or destruction) to the surface of the cathode structure and metal-fuel tape.
Overall, such problems tend to reduce the operational efficiency of prior art metal-air FCB systems, as well as the life of the cathode structures and metal-fuel tape employed therein.
Thus, there is a great need in the art for an improved metal-air fuel cell battery system which avoids the shortcomings and drawbacks of prior art systems and methodologies.
Accordingly, it is a primary object of the present invention to provide an improved metal-air fuel cell battery (FCB) system which avoids the shortcomings and drawbacks of prior art systems and methodologies.
Another object of the present invention is to provide such a system, wherein both the metal-fuel tape, ionically-conductive medium and cathode structures are moved relative to each other during system operation in order to reduce frictional (e.g. shear) forces generated by relative movement among the cathode structure(s), metal-fuel tape and ionically-conductive medium during system operation.
Another object of the present invention is to provide such a system, wherein this reduction in frictional forces results in: a reduction in the amount of electrical power required to drive the cathode structure(s), the metal-fuel tape and ionically-conductive medium during system-operation; a reduction in the shedding of metal-oxide particles from metal-fuel tape and the embedding of such particles within the porous structure of the cathode; and a decrease the likelihood of damage to the cathode structures and metal-fuel tape employed in the system.
Another object of the present invention is to provide such metal-air fuel cell battery system, wherein a transport mechanism is used to transport the cathode structures, ionically-conductive medium and metal-fuel tape at substantially the same velocity at the locus of points at which the ionically-conductive medium contacts both the metal-fuel tape and the cathode structures during system operation in order to minimize the generation of frictional forces between the movable cathode structures, metal-fuel tape and ionically-conductive medium.
Another object of the present invention is to provide such a system, wherein velocity control of the metal-fuel tape, cathode structures and ionically-conducting medium can be realized in a variety of different ways.
Another object of the present invention is to provide such a system, wherein the cathode structure is realized as a rotating cathode cylinder having fine perforations formed in the surface thereof and a hollow central core which enables the transport of oxygen to the interface between the ionically-conductive medium and metal-fuel tape transported thereover.
Another object of the present invention is to provide such a system, wherein the cylindrical cathode comprises a plastic hollow cylinder about which is attached is a cathode element made from nickel mesh fabric, for current collection, embedded within carbon, catalytic and binder material.
Another object of the present invention is to provide such a system, wherein the cylindrical cathode is rotated at a controlled angular velocity and the metal-fuel tape is transported over the surface of the rotating cathode so that both the metal-fuel tape and the cathode structure move at substantially the same velocity at the locus of points at which the ionically-conducing medium contacts both the metal-fuel tape and the cathode structure.
Another object of the present invention is to provide such a system, wherein the ionically-conductive medium is realized in the form of an ionically-conductive belt, transported (i.e. running) between two or more transport cylinders.
Another object of the present invention is to provide such a system, wherein the ionically-conductive belt is fabricated from an open-cell plastic material impregnated with an ionically-conductive material which enables ionic transport between the cathode and anode structures of the system.
Another object of the present invention is to provide such a system, wherein velocity control can be achieved in a variety of ways, for example: by driving the cylindrical cathode structure with a belt that is also used to transport the metal-fuel tape (i.e. between supply and take-up reels or hubs within a cassette type-device); or by driving the cylindrical cathode structure and supply and take-up hubs of a fuel cassette device using a set of speed controlled motors, or spring-driven motors.
Another object of the present invention is to provide such a system, wherein the ionically-conductive medium is realized as a solid-state (e.g. gel-like) film applied on the outer surface of the cylindrical cathode structure, and the metal-fuel tape is realized in the form of thin zinc tape, zinc power mixed with an binder and carried on a polyester substrate, or zinc powder impregnated within the substrate of the tape itself.
Another object of the present invention is to provide metal-air fuel cell battery system, wherein the rotatable cathode structure is realized as a cathode belt structure having ultrafine perforations in the surface thereof and a hollow central core for enabling oxygen transport to the interface between the ionically-conductive medium and the metal-fuel tape transported thereover.
Another object of the present invention is to provide such a system, wherein the cathode belt structure comprises an open-cell type plastic substrate, within which nickel mesh fabric is embedded with carbon and catalytic material.
Another object of the present invention is to provide such a system, wherein during system operation, the cathode belt structure is transported at a controlled velocity between two or more transport cylinders, while metal-fuel tape is transported over the surface of the cathode belt structure at substantially the same velocity at the locus of points at which the ionically-conducing medium contacts both the metal-fuel tape and the cathode structure.
Another object of the present invention is to provide such a system, wherein the ionically-conductive medium of the system is realized in the form of an ionically-conductive belt structure transported between the metal-fuel tape and the cathode belt structure at substantially the same velocity as the cathode belt structure and metal-fuel tape at the locus of points at which the ionically-conducing medium contacts both the metal-fuel tape and the cathode structure.
Another object of the present invention is to provide such a system, wherein the ionically-conductive medium of the system is realized in the form of a thin-film integrated with the outer surface of the cathode belt structure so as to establish contact with the anodic metal-fuel-tape transported thereover.
Another object of the present invention is to provide such a system, wherein the metal-fuel tape is realized in the form of thin zinc tape, zinc power mixed with an binder and carried on a polyester or like substrate, or zinc powder impregnated within the substrate itself.
Another object of the present invention is to provide a metal-air FCB system, wherein the surface tension between the metal-fuel tape and the ionically-conductive medium is sufficiently high (due to wetting of the metal-fuel tape, the ionically-conductive medium and the movable cathode structures) in order to create hydrostatic drag (i.e. hydrostatic attraction) between the metal-fuel tape and the ionically-conductive belt as well as between the cathode structure (e.g. cylinder or belt) and the ionically-conductive medium (e.g. belt or layer), thereby enabling coordinated movement among the metal-fuel tape, cathode structure (e.g. cylinder or belt) and ionically-conductive medium (e.g. belt or layer), with minimal slippage.
Another object of the present invention is to provide a FCB system employing hydrostatic drag between the metal-fuel tape and the ionically conductive medium and between the moving cathode structures and the ionically conductive medium so that all three of these movable system components can be transported (or moved) within the system by moving one or more of such system components (e.g. using spring-driven motor) thereby simplifying and reducing the cost of the system.
Another object of the present invention is to provide a system, wherein the metal-fuel tape, cathode structures and ionically-conductive medium are moved relative to each other so that frictional forces generated among the metal-fuel tape, cathode structures and ionically-conductive medium are substantially reduced, thereby reducing the amount of electrical power required to drive the cathode, metal-fuel tape and ionically-conductive medium and transport mechanisms, and decreasing the likelihood of damage to the cathode structure and metal-fuel tape, and permit reuse thereof over a large number of cycles without replacement.
These and other objects of the present invention will become apparent hereinafter and in the claims to invention.